The present invention relates generally to the field of medical devices for handling radioisotope materials. More specifically, the present invention relates to an automated system for loading low dose radioisotope seeds into implant needles for use in brachytherapy procedures or the like.
The use of radioisotopes for various medical procedures such as brachytherapy and the like is well known. Such uses fall into two general categories: (i) high dose radioisotopes which are temporarily positioned in relation to a patient""s body for a relatively short period of time to effect the radiation treatment, and (ii) low dose radioisotopes which are permanently implanted in a patient""s body with the duration of the radiation treatment determined by the strength and half-life of the radioisotope being implanted. High dose radioisotopes are typically implanted using a catheter arrangement and a device commonly known as an afterloader that advances the high dose radioisotope located on the end of a source wire through the catheter to the desired location. Low dose radioisotopes, on the other hand, are implanted using an array of implant needles with the low dose radioisotopes being encapsulated in very small containers known as seeds that are manually loaded into a series of implant needles and then ejected to form a three-dimensional grid of radioisotopes in the patient that corresponds to a dose plan as determined by the physician. The goal of the low dose brachytherapy procedure is to position this three-dimensional grid of radioisotopes seeds in and around a target cancerous tissue area. Each of the radioisotope seeds consists of a radioactive source such as Iodine (I-125) or Palladium (Pd-103) inside a small tube-like titanium shell that is about the size of a grain of rice. These type of low dose radioactive sources emit a very low energy radiation that is primarily absorbed by the tissue immediately surrounding the radioisotope seed. This constant low energy radiation is typically emitted by the radioisotope seeds for a period of up to six months as a way to kill the cancer cells in the target area without having to subject the patient to the discomfort and risks that often accompany high dose radioisotope procedures.
One common brachytherapy procedure is the use of low dose radioisotopes to treat prostate cancer. Although brachytherapy procedures using low dose radioisotopes can be applied to many different parts of the body, it is helpful to describe a particular treatment to gain a better understanding of these treatments. In a typical prostate cancer procedure, a predetermined number of seeds (between 1-6) are positioned within each of a series of implant needles (up to 40), with the seeds being spaced apart in each needle by small spacers. A small amount of bone wax is positioned on the tip of the implant needles to prevent the seeds and spacers from falling out until they are implanted in the patient. The loaded implant needles are then positioned at the appropriate location for insertion into the perineal area of the patient using a stand that has an X-Y coordinate grid. Each needle is manually positioned in the appropriate chamber in the grid and is inserted into the patient. An ultrasound probe is used to assist the physician in guiding each of the needles to the desired location. The seeds and spacers are delivered from the tip of the implant needle using a stylet and hollow needle arrangement where the hollow needle is preferably retracted while the stylet remains in place. When completed, the implanted seeds form a three-dimensional grid of radioisotope sources that implements a predetermined dose plan for treating the prostate cancer in the patient. For a more detailed background of the procedures and equipment used in this type of prostate cancer treatment, reference is made to U.S. Pat. No. 4,167,179.
Over the years there have been numerous advancements in the design of equipment for use in radioisotope procedures. U.S. Pat. Nos. 4,086,914, 5,242,373 and 5,860,909, as well as PCT Publ. No. WO 97/22379, describe manual seed injector arrangements for a low dose radioisotope procedure that utilize drop-in seed cartridges or seed magazines to supply the seeds directly to an implant needle that is specifically adapted to such cartridges or magazines. Similarly, U.S. Pat. Nos. 4,150,298, 5,147,282, 5,851,172 and 6,048,300 describe replaceable cartridge assemblies that contain the source wire used in conjunction with specifically adapted afterloaders that advance the source wire into a catheter systems for high dose radioisotope procedures.
Although such replaceable cartridges have been well received for use in connection with high dose radioisotope procedures, the standard techniques for low dose radioisotope procedures continue to utilize a series of preloaded implant needles that are manually loaded by a radiophysicist at the hospital just prior to the procedure. There are several reasons for why manual loading of the implant needles just prior to use in low dose radioisotope procedures is preferred. First, there are differences in the types of radioisotope sources that do not favor use of a cartridge arrangement for low dose radioisotope procedures. The source wires used for high dose radioisotope procedures use only one or a small number of very high power radioisotope sources having relatively long half-lives. As a result, it is cost effective and practical to provide for a cartridge arrangement for such a small number of high dose radioisotopes that can be preordered and maintained at the hospital well in advance of a procedure. In contrast, given the relatively short half-lives of the radioisotopes used in low dose radioisotope procedures it is preferable that the radioisotope seeds be sent to the hospitals just prior to their use. Because the number of radioisotope seeds varies from procedure to procedure depending upon the dose plan and because the cost of each low dose radioisotope seed is significant, it is not cost effective to order many more radioisotope seeds than will be used in a given procedure. Second, it is important to minimize the time of the procedure, both in terms of the exposure time of the physician to the low dose radioisotope seeds and in terms of the total time of the procedure from the economics of medical practice. The existing drop-in cartridge and seed magazine systems described above take longer to perform the implant procedure than using conventional preloaded implant needles because the radioisotope seeds are implanted one-by-one, rather than being delivered simultaneously as a group from a preloaded needle. Third, it has been routine to employ a radiophysicist at the hospital to preload the implant needles and take a set of sample measurements of the strength of the radioisotope seeds to confirm that the seeds meet the requirements specified by the dose plan. Finally, due to the large number of low dose radioisotope seeds used in a given procedure (typically up to 150) and the need for the implanting physician to be able to modify the dose plan at the time of implant, it is generally considered that the flexibility afforded by manually loading the implant needles just prior to the operation provides the best possible treatment procedure for the patient and the most economically efficient procedure for the hospital.
Although manual preloading of implant needles at the hospital continues to be the norm for most low dose radioisotope procedures, relatively little attention has been paid to increasing the safety or efficiency of this process. Presently, the radioisotope seeds for a given dose plan are shipped in bulk in a protective container to the hospital. At the hospital, the radioisotope seeds are dumped from the container onto a tray where the radiophysicist manually loads the seeds one-by-one into a set of implant needles according to the dose plan. Typically, the implant needles are positioned tip into a needle stand with the tips sealed with bone wax. The radiophysicist picks up a single radioisotope seed using a tweezers, forceps or vacuum hose and deposits that seed in a needle. Next, a single spacer made of gut or similar absorbable material is deposited in the needle. This process is repeated depending upon the predetermined number of seeds and spacers prescribed by the dose plan. The radiophysicist will use a well chamber to measure the strength of a sample of the radioisotope seeds (typically from only one seed to a sample of about 10%). While some needle stands are provided with a certain degree of shielding once the radioisotope seeds are loaded in the implant needles, there is very little shielding that protects the hands and fingers of the radiophysicist during the process of manually loading the implant needles.
U.S. Pat. No. 4,759,345 describes a radiation shielded seed loader for hand implanted hypodermic needles that uses a shielded cylindrical container to house up to seven implant needles. The implant needles have their tips sealed with bone wax and are placed into chambers in an alignment disc. A seed loading disc is located above the ends of the needles and is oriented with each of seven funnels located above a respective end of the needle. The loading procedure occurs behind an L-shaped shielding block and requires the use of a forcep to pick up seeds one at a time and drop them into one of the funnels to be guided into the end of the respective needle. Once each of the needles has been loaded through the funnels in the seed loading disc, the seed loading disc is removed and a plunger is inserted into each needle. Finally, a spacer key distances a cover plate from the ends of the plungers to prevent the plungers from accidentally discharging the seeds during transport. With the cover plate in place, the entire cylindrical container is ready to be transported. Although this type of seed loader would allow for the remote loading of implant needles to be transported in a preloaded fashion to the hospital, if the seeds fall out of the implant needles during shipping or removal of the needles from the container, it is difficult to locate and reload the seeds. The fact that different physicians prefer different types of implant needles further complicates the desirability of using this type of preloaded container.
U.S. Pat. No. 5,906,574 describes a vacuum-assisted apparatus for handling and loading radioisotope seeds within a visible radiation shield. A shielded container with a lead glass window has a vacuum probe that can manipulate and pick up individual seeds. The outlet of the vacuum probe is connected to a lead glass tube such that the operator can verify that the correct sequence of seeds and spacers has been arranged in the lead glass tube. Once the correct sequence has been visually verified, the tip of an implant needle is positioned in a slip shield body and docked on the other end of the lead glass tube. A vacuum force is applied to the back end of the implant needle to suck the seeds and spacers into the implant needle. The implant needle is then undocked from the glass tube and bone wax is used to seal the tip. Once the tip is sealed, the vacuum source is removed from the rear end of the needle and a stylet or plunger is inserted into the needle. The loaded needles with the protective slip shield are placed in a needle holder box until they are to be implanted. While this apparatus improves upon the shielding and safety of the manual process of preloading implant needles, it does not offer any significant improvements to the efficiency of the process.
The same company which provides the vacuum-assisted apparatus for handling and loading radioisotope seeds described in U.S. Pat. No. 5,906,574, also provides several other manual and simple mechanical devices that can be used as part of a manual needle loading process, including a brachytherapy well chamber for taking radiation measurements, an Indigo(trademark) express seeding cartridge for use with the well chamber, a Rapid Strand(trademark) seed carrier as described in U.S. Pat. Nos. 4,815,449 and 4,763,642 which prepositions and encases a series of seeds in a body absorbable material, a seed sterilization and sorting tray, a seed alignment tray, a seed sterilization box, a seed slider for loading needle, and various needle cradles and holders. The Indigo(trademark) express seeding cartridge which is a tube with seeds prepositioned in the tube is only used to accurately index and position individual seeds in the well chamber of a radiation detector for purposes of calibrating the radioisotope seeds. The seed slider interfaces with the seed sterilization and sorting tray that has a seed reservoir for receiving batches of seeds in different wells and sorting area and loading platform. A user scoops seeds from the wells onto the loading platform with the provided spatula. The user then align the seeds and spacers into a slot per treatment prescription. A cover then flips up to encapsulate the seeds and spacers. The needles to be loaded are locked onto one side of the seed slider with a Luer lock. A needle stylet is inserted into the other side of the seed slider and the seeds and spacers are pushed into the treatment needle.
Despite these improvements, the manual loading of implant needles for low dose radioisotope procedures remains a cumbersome process that can expose radiophysicists and other hospital personal to unshielded radioisotopes. It would be advantageous to provide for a system for loading implant needles for low dose radioisotope procedures that could overcome these problems and enhance the safety and efficiency of this process.
The present invention is an automated system for loading low dose radioisotope seeds into a plurality of implant needles. The automated system is comprised of a loading station into which a replaceable cartridge may be positioned. The cartridge contains a plurality of radioisotope seeds and a plurality of spacers preloaded into the cartridge. The cartridge has at least one aperture and preferably the radioisotope seeds and spacers are loaded around the periphery of a rotatable drum within the cartridge. The loading station has a cartridge receiving structure and an automated motion control system. When the cartridge is positioned in the cartridge receiving structure, the automated motion control system preferably drives a pair of stepper motors within the cartridge, one for rotating the rotatable drum and one for sliding a pushrod to selectively eject radioisotope seeds and spacers from the cartridge into each of a plurality of implant needles. In one embodiment, the implant needles are positioned rear first into the loading station. In another embodiment, the implant needles are positioned tip first into the loading station. Once a predetermined arrangement of radioisotope seeds and spacers are loaded into the implant needle, a plug is positioned in the tip of the implant needle. Preferably, the automated system includes a computer processor having a touch screen user interface that is connected to and directs the operation of the automated motion control system to load the plurality of implant needles in accordance with a predetermined dose plan.
In a preferred embodiment, the cartridge receiving structure is defined in a front side of the loading station oriented toward a user. Several features of the preferred embodiment improve the ease of operation and minimize the potential for misalignment within the automated system. The cartridge receiving structure defines a downwardly angled path of travel for inserting the cartridge into the cartridge receiving structure. The interface between the cartridge and the cartridge receiving structure is primarily an electrical connection in the preferred embodiment as the stepper motors and associated encoder discs are contained within the cartridge, thereby minimizing the need for extremely tight tolerance matches between the cartridge receiving structure and the cartridge. Once in position, the loading station locks the cartridge in place using an electrical solenoid to prevent inadvertent removal.
Preferably, the cartridge includes a machine readable storage medium, such as an EEPROM, that stores indicia representing at least the quantity and location of the radioisotope seeds preloaded in the cartridge. The computer processor in the automated system is preferably provided with a machine readable format of the predetermined dose plan. The computer processor is programmed to use the information in the EEPROM and the predetermined dose plan in a dynamic fashion so as to cause the automated motion control system to selectably position the rotatable drum in the cartridge relative to the aperture and eject the proper number of radioisotope seeds and spacers into each needle in accordance with a predetermined dose plan. Optionally, a user can interact with the user interface of the computer system to alter the predetermined dose plan during the process of loading the implant needles if necessary. Preferably, the touch screen interface displays a graphic representation of the coordinates of each needle to be loaded, with the user selecting the next needle to be loaded by touching one of the coordinates. As the coordinate is touched, the icon associate with that coordinate would change color indicating that that needle had been loaded. In addition, as each needle is loaded, a graphic representation of a cross-section of the needle is displayed to allow a user to confirm visually the proper loading of radioisotope seeds and spacers within the implant needle.
In a preferred embodiment, a position sensor along the path of the push rod is used to detect and register the position of the tip of the pushrod to monitor and confirm the proper loading of radioisotope seeds and spacers in to the implant needle. Further confirmation of the proper loading of the radioisotope seeds can be accomplished by a radiation sensor that detects a radiation level of the radioisotope seeds after they are ejected from the cartridge. Unlike existing systems which make only sample measurements of radiation levels, the present invention can confirm the properly radiation level of each radioisotope seed. Alternatively, a user may select to monitor the radiation level of only the first radioisotope seed ejected into an implant needle or only a given number of the radioisotope seeds.
As a further enhancement of the flexibility of the present invention, different sized spacers may be utilized with the present invention. In one embodiment, spacers loaded into the cartridge may be either a full-length spacer or a smaller-length spacer, where the full-length spacer has a length slightly longer than the length of a radioisotope seed. The use of a smaller-length spacer is advantageous in certain circumstances where it is desirable to offset the spacing of the radioisotope seeds in adjacent planes of the predetermined dose plan. Presently, the only way to accomplish this is by having the radio physicist manually cut a portion from a full-length spacer prior to loading it into an implant needle. Typically, a radioisotope seed for a prostate cancer procedure will have a length of 4.5 mm, with a full-length spacer having a length of approximately 5.5 mm. Although this embodiment is preferably contemplated in terms of using full-length and half-length spacers, the present invention affords the ability to customize the length of the smaller-length spacers as desired. In another embodiment, a special size spacer referred to as a blank is provided that has a length equal to the length of a radioisotope seed. Blanks are used to maintain spacing of adjacent planes in a dose plan by allowing a given location that should contain a seed in a typical seedxe2x80x94spacerxe2x80x94seed xe2x80x94spacer arrangement to contain a blank in the place of a seed without altering the longitudinal spacing of this typical arrangement.
In an alternate embodiment, the stepper motors for driving the rotatable drum and the pushrod are located in the loading station, instead of in the replaceable cartridge. In this embodiment, the front side of the loading station includes a pivotable door that operates in a close positioned as a shield when the cartridge is positioned in the cartridge receiving structure and in an open position as a tray for retaining loose radioisotope seeds and spacers. When the cartridge is in position in the cartridge receiving structure, a first drive wheel and a position encoder in the cartridge are operably engaged by a second drive wheel and a position sensor in the loading station to drive and sense the position of the rotatable drum in the cartridge. A position registration mechanism preferably positions the cartridge within the cartridge receiving structure within the tolerance of +/xe2x88x920.010 inches. Preferably, the position registration mechanism comprises a ball and detent mechanism with cartridge having at least one detent defined on our surface and a loading station having a cam driven ball mechanism that selectively seats at least one ball in the least one detent to properly register the position of the cartridge within the cartridge receiving structure. The loading station also includes at least one guide rail having a push rod connected to a linear actuator that is controlled by the automated motion control system to selectively eject the radioisotope seeds and spacers from the periphery of the rotatable drum of the cartridge.
The automated system of the present invention advantageously uses a replaceable cartridge to transport and dispense the radioisotope seeds in a manner much safer and more efficient than current conventional manual practices. The replaceable cartridge. is provided with sufficient shielding to insure safe handling of the low dose radioisotope seeds. The positioning of the radioisotope seeds around the periphery of a rotatable drum within the replaceable cartridge further serves to minimize safety issues by preventing a buildup of radioisotope seeds at any one location within the cartridge.